arXiv subjects

I. Felner

Publications and source records attributed to I. Felner.

52 records · Page 3Linked to original sources

arXiv2003

Competition of Superconductivity and Magnetism in MoSr2R1.5Ce0.5Cu2O10-d (R=Rare-earth, Mo-1222)

We have investigated the MoSr2R1.5Ce0.5Cu2O10-d (Mo-1222R, R=rare earth) system by several complementary experimental techniques. In contrast to the iso-structural RuSr2R1.5Ce0.5Cu2O10-d (Ru-1222) system, in which superconductivity (SC) in the CuO2 planes and weak-ferromagnetism in the Ru sub-lattice coexists, in Mo-1222, displays a competition between the two states, namely, SC vanishes when the magnetic order sets in. The contraction in the R elements leads to a change of the physical states. The light R ions (Pr and Nd) are paramagnetic down to 5 K, whereas the middle R ions (Sm and Eu) are SC at TC 18-23 K respectively. The SC charge carriers originate from the CuO2 planes, and annealing under oxygen pressures does not affect TC. A simple model for the SC state is proposed. For the heavy R elements Ho-Lu and Y, the pentavalent Mo layers are antiferromagnetically (AFM) ordered at TN ranging from 13-26 K. For R=Gd, the sample is not SC and exhibit two magnetic transitions at 11 and 184 K. Both the SC or AFM states depend strongly on the R/Ce ratio and for R/Ce=1, both states are suppressed.

cond-mat.supr-con↗

arXiv2003

Magnetization study of RuSr2Y1.5Ce 0.5Cu2O10 (Ru-1222)

We have studied the magnetic properties of the non-superconducting RuSr2Ln1.5Ce0.5Cu2O10 (Ln=Y, Dy and Ho, Ru-1222) compounds synthesized under high pressure (6 Gpa) at elevated temperature. The materials become magnetically ordered at TM =152(2) K regardless of Ln. The wide ferromagnetic-like hysteresis loops which open at 5 K, close themselves around Tirr= 90-100 K and the remanent magnetizations (Mrem) and the coercive fields (HC) become zero. Surprisingly, at Tirr<T< TM a reappearance of the Mrem and HC (with a peak at 120-130 K) is observed for all three samples studied. For the non-magnetic Ln=Y compound, the extracted saturation moment at 5 K and the effective paramagnetic moment are is 0.75 and 2.05 mB /Ru, values which are close to the expected 1 mB and 1.73 mB respectively, for the low-spin state of Ru5+. We argue that the Ru-1222 system becomes (i) anti-ferromagnetically (AFM) ordered at TM. In this range a metamagnetic transition is induced by the applied field (ii). At Tirr < TM, weak-ferromagnetism (W-FM) is induced by the canting of the Ru moments.

cond-mat.str-el↗

arXiv2003

On the effect of heterovalent substitutions in ruthenocuprates

We discuss the properties of superconducting derivatives of the RuSr2GdCu2O8 (1212-type) ruthenocuprate, for which heterovalent doping has been achieved through partial substitution of Cu ions into the RuO2 planes (Ru1-xSr2GdCu2+xO8-d, 0 Ru doping achieved in these phases is found to decrease the temperature for magnetic ordering as well the volume fraction of the magnetic phase.

cond-mat.supr-con↗

arXiv2002

Coexistence of Superconductivity and Magnetism in R2-xcexrusr2cu 2o10-? (R=Eu and Gd)

R2-xCexRuSr2Cu2O10-d(Ru-2122) is the first Cu-O based system in which superconductivity (SC) in the CuO2 planes and weak-ferromagnetism (W-FM) in the Ru sublattice coexists. The hole doping in the CuO2 planes, is controlled by appropriate variation of the Ce concentration and/or increasing the oxygen concentration. In Eu2-xCexRuSr2Cu2O10, SC occurs for Ce contents of 0.4-0.8, with the highest TC=35 K for Ce=0.6. The as-prepared non-SC EuCeRuSr2Cu2O10 sample exhibits magnetic irreversibility below Tirr=125 K and long range o anti-ferromagnetic (AFM) order at TM =165 K. The saturation moment at 5 K is Msat=0.89 mB /Ru. Annealing under oxygen pressures, does not affect these parameters, whereas depletion of oxygen shifts both Tirr and TM up to 169 and 215 K respectively. TM, Tirr and Msat decrease with x, and the Ce dependent magnetic-SC phase diagram is presented. A simple model for the SC and the long-range W-FM states is proposed. We argue that: (i) the system becomes AFM ordered at TM; (b) at Tirr < TM, W-FM is induced by the canting of the Ru moments, and (c), at lower temperatures the appropriate samples become SC at TC. The magnetic features are not affected by the SC state, and the two states coexist.

cond-mat.supr-con↗

arXiv2002

Magnetic studies of Ca1-xMxRuO3 (M=La and Sr)

CaRuO3 is a perovskite with an orthorhombic distortion and shows the characteristics of spin-glass behavior below TC=87 K. The La3+ substitution for Ca2+ in Ca1-xLaxRuO3 samples, induces a disorder in the Ca site (the A site) and the system becomes antiferromagnetically (AFM) ordered with TN = 58 and 19 K for x=0.1 x=0.5 respectively. In the Ca1-xSrxRuO3 system, the Ca0.8Sr0.2RuO3 sample is canted-AFM ordered at 107 K. The compounds with higher Sr concentration display ferromagnetic behavior and the saturation moment increases with Sr. Huge magnetic hysteresis loops are obtained at low temperatures. The coercive field (HC) decreases with Sr. For x=0.4 HC =9.5 kOe (at 5 K) whereas for SrRuO3 HC =2.4 kOe. For x=0.4 and 0.6, HC decreases sharply with temperature and than increases again with a peak at 95 and 115 K, respectively. On the other hand, for SrRuO3, HC remains practically unchanged up to 50 K and shows a peak at 90 K and than decrease sharply up to TC =165 K.

cond-mat.supr-con↗

arXiv2001

Disorder and thermally driven vortex-lattice melting in La{2-x}Sr{x}CuO{4} crystals

Magnetization measurements in La{2-x}Sr{x}CuO{4} crystals indicate vortex order-disorder transition manifested by a sharp kink in the second magnetization peak. The transition field exhibits unique temperature dependence, namely a strong decrease with temperature in the entire measured range. This behavior rules out the conventional interpretation of a disorder-driven transition into an entangled vortex solid phase. It is shown that the transition in La{2-x}Sr{x}CuO{4} is driven by both thermally- and disorder-induced fluctuations, resulting in a pinned liquid state. We conclude that vortex solid-liquid, solid-solid and solid to pinned-liquid transitions are different manifestations of the same thermodynamic order-disorder transition, distinguished by the relative contributions of thermal and disorder-induced fluctuations.

cond-mat.supr-con↗

arXiv2001

The magnetic behavior of Li2MO3 (M=Mn, Ru and Ir) and Li2(Mn1-xRux)O3

The present study summerizes magnetic and Mossbauer measurements on ceramic Li2MO3 M= Mn, Ru and Ir and the mixed Li2(Mn1-xRux)O3 materials, which show many of the features reflecting to antiferromagnetic ordering or to existence of paramagnetic states. Li2IrO3 and Li2RuO3 are paramagnetic down to 5 K. Li2(Mn1-xRux)O3 compounds are antiferromagnetically ordered at TN = 48 K for x=0. TN decreases as the Ru content increases and, for x=0.8, TN =34 K.

cond-mat.mtrl-sci↗

arXiv2001

Itinerant-electron Ferromagnetism in W(Nb)O3-d

The crystal structure and the magnetic properties of the W1-xNbxO3-d, (x<0.03) system have been investigated. In contrast to the orthorhombic diamagnetic WO3, the material with x=0.01 is paramagnetic down to 5 K. Introducing of 2.5 at. % of Nb into WO3 leads to a tetragonal structure and to a weak itinerant ferromagnetic ordering below TC= 225 K. The saturation magnetic moment at 5 K is 1.07*10-3 mB, whereas the paramagnetic effective moment is 0.06 mB per mole. This high ratio indicates itinerant ferromagnetism in W0.975Nb0.025O3-d.

cond-mat.mtrl-sci↗

arXiv2001

Magnetic-Superconducting phase-diagram of Eu2-xCexRuSr2Cu2O10

Eu2-xCexRuSr2Cu2O10-d (Ru-2122) is the first Cu-O based system in which superconductivity (SC) in the CuO2 planes and weak-ferromagnetism (W-FM) in the Ru sub-lattice coexists. The hole doping in the CuO2 planes, is controlled by appropriate variation of the Ce concentration. SC occurs for Ce contents of 0.4-0.8, with the highest TC=35 K for Ce=0.6. The as-prepared non-SC EuCeRuSr2Cu2O10 (x=1) sample exhibits magnetic irreversibility below Tirr=125 K and orders anti-ferromagnetically (AFM) at TM =165 K. The saturation moment at 5 K is Msat=0.89 mB /Ru close to the expected 1 mB for the low-spin state of Ru5+. Annealing under oxygen pressures, does not affect these parameters, whereas depletion of oxygen shifts both Tirr and TM up to 169 and 215 K respectively. Systematic magnetic studies on Eu2-xCexRuSr2Cu2O10-d show that TM, Tirr and Msat decrease with x, and the Ce dependent magnetic-SC phase diagram is presented. A simple model for the SC state is proposed. We interpret the magnetic behavior in the framework of our ac and dc magnetic studies, and argue that: (i) the system becomes AFM ordered at TM; (b) at Tirr < TM, W-FM is induced by the canting of the Ru moments, and (c), at lower temperatures the appropriate samples become SC at TC. The magnetic features are not affected by the SC state, and the two states coexist.

cond-mat.supr-con↗

arXiv2001

Ruthenocuprates RuSr2(Eu,Ce)2Cu2O10: Intrinsic magnetic multilayers

We report ac susceptibility data on RuSr_2(Eu,Ce)_2Cu_2O_(10-y) (Ru-1222, Ce content x=0.5 and 1.0), RuSr_2GdCu_2O_8 (Ru-1212) and SrRuO_3. Both Ru-1222 (x=0.5, 1.0) sample types exhibit unexpected magnetic dynamics in low magnetic fields: logarithmic time relaxation, switching behavior, and `inverted' hysteresis loops. Neither Ru-1212 nor SrRuO_3 exhibit such magnetic dynamics. The results are interpreted as evidence of the complex magnetic order in Ru-1222. We propose a specific multilayer model to explain the data, and note that superconductivity in the ruthenocuprate is compatible with both the presence and absence of the magnetic dynamics.

cond-mat.supr-con↗

arXiv2001

Giant nonlinear response of superconducting single crystal niobium in a sweeping magnetic field

Giant enhancement of the nonlinear response of a single crystal of Nb placed in a sweeping magnetic field has been experimentally observed. The rectified signal from Nb ($Tc=9.15$ K) has been measured by means of an inductive method as a function of temperature, dc field, dc field sweep rate, and the amplitude of ac field. The Nb sample was excited by an amplitude modulated ac field. Under a stationary regime, the rectified signal appears only for magnetic fields ($H_0$) in the range $H_{c2} H_{c1}$. This experiment shows that the amplitude of the rectified signal is two orders of magnitude larger than the amplitude of the signal seen under stationary field conditions. Moreover, the amplitude of the rectified signal is a power function of the sweep rate, with the power exponent close to 1.

cond-mat.supr-con↗

arXiv2001

Ruthenocuprates: Intrinsic magnetic multilayers

We report ac susceptibility measurements on polycrystalline samples of SrRuO_3 and three ruthenocuprates: superconducting RuSr_2GdCu_2O_8 (Ru-1212), superconducting RuSr_2Eu_(2-x)Ce_xCu_2O_y (Ru-1222, x=0.5) and nonsuperconducting, insulating RuSr_2Eu_(2-x)Ce_xCu_2O_z (Ru-1222, x=1.0). Ac susceptibility of both Ru-1222 compositions exhibit logarithmic time relaxation and `inverted' hysteresis loops. Ru-1212 samples exhibit none of these behaviors. We interpret the magnetic behavior of Ru-1222 in the framework of weakly coupled magnetic multilayers and argue that superconductivity coexists with qualitatively different magnetic behaviors.

cond-mat.supr-con↗

arXiv2001

On the Magnetism of the Normal State in MgB2

The experimentally observed ferromagnetism in MgB2 in the normal state is attributed to micro phase separated inclusions of iron. This magnetic character is also observed when the iron content of the samples is reduced below 20 micro-g/g, however in these samples the diamagnetism of MgB2 is apparent and is measured. It is found experimentally that the diamagnetic susceptibility at room temperature of B element, MgB2 and MgB4 is close to the ratio 1:2:4, suggesting that the diamagnetism in these borides is confined to the boron atoms. This observation supports a picture in which the two electrons of Mg are donated to B in MgB2

cond-mat.supr-con↗

arXiv2001

Metal-to-insulator transition and magnetic ordering in CaRu_{1-x}Cu_xO_3

CaRuO_3 is perovskite with an orthorhombic distortion and is believed to be close to magnetic ordering. Magnetic studies of single crystal and polycrystalline CaRu_{1-x}Cu_xO_3 (0\le x \le 15 at.%Cu) reveal that spin-glass-like transition develops for x\le 7 at.%Cu and obtained value for effective magnetic moment p_{eff}=3.55 mu_B for x=5 at.% Cu, single crystal, indicates presence of Ru^{5+}. At higher Cu concentrations more complex magnetic behaviors are observed. Electrical resistivity measured on polycrystalline samples shows metal-to-insulator transition (MIT) at 51 K for only 2 at.% Cu. Charge compensation, which is assumed to be present upon Cu^{2+/3+} substitution, induces appearance of Ru^{5+} and/or creation of oxygen vacancies in crystal structure. Since the observed changes in physical properties are completely attributable to the charge compensation, they cannot be related to behaviors of pure compound where no such mechanism is present. This study provides the criterion for "good" chemical probes for studying Ru-based perovskites.

cond-mat.str-el↗

arXiv2001

Linear and Nonlinear Ac Response of MgB2 Superconductors

We report the experimental study of linear and nonlinear ac properties of two types of samples of MgB2 prepared by different technologies. A commercial sample (Alfa Aesar) demonstrates two stages of a broad phase transition, whereas home-made metallic sample have one sharp transition. The temperature dependence of the rectified signal shows two peaks for the commercial and one peak for the metallic samples. Two types of weak links (intergrain and intragrain) are responsible for the nonlinear response of these samples. The properties of these weak links are discussed.

cond-mat.supr-con↗

arXiv2000

A nature of low-temperature resistivity minimum in ceramic manganites

Measurements of magnetoresistance and magnetization were carried out on ceramic samples of La_{0.5}Pb_{0.5}MnO_{3} and La_{0.5}Pb_{0.5}MnO_{3}, containing 10 at. % Ag in a dispersed form. The results obtained for the resistivity at zero applied magnetic field exhibit a shallow minimum at temperatures T about 25 K - 30 K, which shifts towards lower temperatures upon applying magnetic field and disappears at a certain (rather low) field. Also the resistivity at helium temperature decreases upon applying magnetic fields. It is shown that the model of spin-dependent carrier tunneling between antiferromagnetically coupled grains may account for the results observed.

cond-mat.dis-nn↗